1. Field of Invention
The present invention relates to a semiconductor structure and a method of forming the same, and more generally to a semiconductor structure including a resistor and a metal gate structure and a method of forming the same.
2. Description of Related Art
As the dimension of a semiconductor device is getting smaller, the dimension of the gate structure and the thickness of the gate insulation layer are reduced accordingly. However, a leakage current occurs when the gate insulation layer of silicon oxide becomes thinner. To reduce the leakage current, a high dielectric constant (high-k) material is used to replace silicon oxide for forming the gate insulation layer. The gate of polysilicon may react with the high-k material to generate a Fermi-level pinning, so that the threshold voltage is increased and the performance of the device is affected. Therefore, a metal layer (i.e. so-called work function metal layer) is used as a gate, so as to avoid an increase in the threshold voltage and reduce the resistance of the device.
The metal gate process is usually integrated with the process of forming a voltage divider such as a resistor. As the design rule of the semiconductor device is scaled down, the standard for the resistor in the metal gate process is accordingly increased. Therefore, how to fabricate a resistor with good performance in the metal gate process has been one of the main topics in the industry.